1. Field of the Invention
The present application relates to a method and apparatus for selectively detecting gaseous compounds.
2. Background of the Art
There has been an increasing demand for electronic instruments that can mimic the human olfactory processes and which may provide low-cost and rapid sensory information to hasten the process of evaluation of odors. This led to the conceptualization of an electronic nose (“e-nose”) as an intelligent chemical array sensor system for odor classification. At the same time the need for biochemical detectors that are able to sense the presence of pathogens in humans and which can contribute to the early detection of diseases is high.
Although analysis of body fluids (blood, sputum, urine) for disease diagnoses and monitoring is routine clinical practice, human breath analysis methodologies that exploit the non-invasive nature of such diagnoses are still under-developed. Since antiquity, such as the time of Hippocrates, exhaled breath was known to enable non-invasive detection of disease.
Breath testing devices first appear in 1784 when Lavoisier detected CO in the exhaled breath of guinea pigs. Since then, colorimetric assays and gas chromatography columns have been used to detect VOCs (volatile organic compounds) in (human) breath in quantities varying from millimolar (10−3M) to picomolar (10−12M) concentrations. The latter gas sensitivity limit was achieved by Linus Pauling's gas-chromatography-based breath analysis device in 1971. Among the 400 compounds of which the human breath consists, only 30 have been identified by GC/MS.
Various apparatus and methods for olfactometry are disclosed in U.S. Pat. Nos. 6,841,391, 6,839,636, 6,820,012, 6,767,732, 6,703,241, 6,620,109, 6,609,068, 6,606,566, 6,467,333, 6,411,905, and 6,319,724, all of which are incorporated herein by reference. A transition metal oxide gas sensor is disclosed and described in U.S. Pat. No. 6,173,602, which is herein incorporated by reference.
There are various medical uses for “e-nose” sensors. Gas odors evolving from infections or disorders provide the pathway for chemical sensors to be used in biochemical applications. NO2 is a gas associated with bronchial epithelial infection arising out of tobacco smoking. Ammonia is a product of decomposition of urea. Hence, chemical sensors capable of detecting these chemical species can be easily used for medical applications. The key deficiency of current sensor/e-nose technologies is the lack of specificity in recognizing the particular analyte/gas detected.